1. Field of the Invention
This invention relates generally to controlling a powertrain of a vehicle having all-wheel drive capability and an automatic engine stop-restart function.
2. Description of the Prior Art
Many of the vehicles that are equipped with an automatic stop-restart function are also being equipped with an All-Wheel Drive (AWD) powertrain or 4×4 powertrain, which is re-actuated either automatically or manually in response to customer selection. The automatic stop-restart function is a fuel saving strategy whereby a vehicle controller automatically turns the engine off when the vehicle is stopped and the engine is idling.
Other fuel saving strategies or systems may be fully or partially incompatible with AWD/4×4-operation. For example, while the vehicle's engine is auto-stopped, 4×4/AWD operation may be requested by the vehicle operator or by an automated system responding to vehicle usage, road, weather, or other operating conditions. When this occurs, system incompatibilities can arise if activation of off-road components occurs while the engine is off due to lack of available electrical energy or insufficient engine rotation or torque or if activation occurs immediately prior to an automatic stop-restart induced auto-restart. The energy required to operate high current components may be greater than available electrical thresholds required to support engine cranking concurrently with activation of high current AWD/4×4 mechanisms.
Even while the engine is running, it is beneficial to have the stop-restart function react to detection of AWD/4×4 activation or identification of a need for such activation so as to inhibit subsequent stop-restart actions in favor or supporting off-road operation and device activations.
The opposite is also true, it may be beneficial to favor fuel economy modes such as stop-restart actions when the AWD/4×4-operation is deactivated or conditions support deactivation of off-road operating modes.